Section 1.3.2Unit 1: Markets in Action
Unit 1: Markets in Action
Consumer Behaviour & Demand
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Traditional economics assumes consumers weigh up costs and benefits at the margin and choose the option that maximises their satisfaction.
A rational economic agent is one who considers all available information and chooses the option that gives the greatest net benefit. For consumers this means maximising utility (satisfaction); for firms it means maximising profit. Every decision is made at the margin — you compare the extra benefit of one more unit against its extra cost.
Rational decision-making requires that you have complete information, can process it instantly, and are not swayed by emotion or habit. In reality, those conditions rarely hold — but the assumption is useful because it gives economists a benchmark to predict how people tend to behave in competitive markets.
Real Example: When Aldi entered the UK grocery market with rock-bottom prices, the rational-consumer model predicted shoppers would switch from Tesco and Sainsbury's to save money. That is broadly what happened — Aldi's UK market share rose from 2% in 2010 to over 10% by 2023.
Exam Matters: Examiners often open a paper with a short question on rational decision-making. Define it as maximising utility by comparing marginal benefit to marginal cost, then note it is an assumption, not a description of how everyone actually behaves.
Utility is the satisfaction a consumer gains from consuming a good — you maximise it when the last pound spent on every good gives equal marginal utility.
Utility is the economist's word for satisfaction or benefit. Total utility is the overall satisfaction from all units consumed. Marginal utility is the extra satisfaction from consuming one more unit. As you keep consuming the same good, marginal utility typically falls — this is the law of diminishing marginal utility.
A consumer maximises total utility when the marginal utility per pound spent is equal across all goods: MU_A / P_A = MU_B / P_B. If a pound spent on coffee gives you more satisfaction than a pound spent on tea, you should buy more coffee and less tea until the two ratios equalise.
Real Example: Domino's "Two for Tuesday" deal exploits diminishing marginal utility. Your first pizza delivers high satisfaction, but a second is worth much less to you. Domino's prices the bundle cheaply enough that even the lower marginal utility of pizza two still exceeds the marginal cost you pay.
Exam Matters: If a question says "explain how a consumer maximises utility," the examiner wants the equi-marginal condition: MU_A/P_A = MU_B/P_B. Show that if the ratios are unequal, the consumer can increase total utility by reallocating spending.
Real people use mental shortcuts, are swayed by emotions and habits, and lack perfect information — behavioural economics explains these systematic departures from rationality.
Behavioural economics shows that consumers systematically deviate from the rational model. People rely on heuristics (mental shortcuts), are influenced by anchoring (fixating on the first number they see), and exhibit loss aversion (losses hurt roughly twice as much as equivalent gains feel good).
You also face bounded rationality — your brain cannot process all available information, so you settle for a "good enough" choice rather than the optimal one. Habits, peer pressure, advertising, and addiction all push behaviour away from the rational ideal.
Real Example: Apple exploits anchoring by showing the most expensive iPhone first on its website. When you then see the mid-range model, it feels like a bargain by comparison — even though it is still expensive in absolute terms. This is a systematic departure from rational price comparison.
Exam Matters: Evaluation questions love this topic. If you argue consumers are rational, counter-argue with behavioural biases and vice versa. Name specific biases (anchoring, loss aversion, bounded rationality) rather than vaguely saying "people are irrational."
Demand is the quantity consumers are willing and able to buy at each price — the curve slopes downward because higher prices make you buy less.
Demand is not just wanting something — it is the quantity of a good or service that consumers are willing and able to purchase at each given price in a given time period. If you want a Porsche but cannot afford one, that is desire, not demand. Demand requires both willingness and ability to pay.
The demand curve slopes downward from left to right, showing a negative (inverse) relationship between price and quantity demanded. There are two explanations. The income effect: when price falls, your real income rises so you can buy more. The substitution effect: when price falls, the good becomes cheaper relative to alternatives so you switch towards it.
Real Example: When Samsung cut the price of its Galaxy A-series phones by 20%, sales volumes jumped significantly in emerging markets. Consumers who previously bought cheaper brands substituted towards Samsung (substitution effect), while existing Samsung users upgraded sooner (income effect).
Exam Matters: The distinction between a movement along the demand curve and a shift of the curve is tested relentlessly. If the question mentions a price change of the good itself, it is a movement along. If it mentions any other factor, it is a shift. Always state which one clearly.
A change in the good's own price causes a movement along the demand curve; a change in any other factor shifts the whole curve left or right.
A movement along the demand curve is caused by a change in the good's own price — nothing else. A price rise causes a contraction (movement up and left). A price fall causes an extension (movement down and right). The curve itself does not move.
A shift of the demand curve means that at every price, consumers want to buy a different quantity. The entire curve moves left (decrease in demand) or right (increase in demand). This is caused by changes in factors other than the good's own price.
Real Example: When Starbucks raises the price of a latte from £3.50 to £4.00, fewer lattes are sold — a contraction along the demand curve. But when a viral social-media health scare about coffee emerged, demand for lattes fell at every price — the whole curve shifted left.
Exam Matters: Diagram questions almost always test this distinction. Label your diagram clearly: if you show a movement, mark the old and new points on the same curve. If you show a shift, draw two separate curves (D1 and D2) and label both.
Income, tastes, prices of related goods, population size and expectations about the future all shift the demand curve — use the mnemonic ITPSE.
Several non-price factors shift the demand curve. Income: if incomes rise, demand for normal goods increases (shifts right) while demand for inferior goods decreases (shifts left). Tastes and preferences: advertising, trends and health awareness all change what consumers want.
Prices of related goods matter too. If the price of a substitute rises, demand for your good shifts right (consumers switch). If the price of a complement rises, demand for your good shifts left (the pair is bought together). Population growth shifts demand right simply because there are more buyers.
Expectations can also shift demand. If consumers expect prices to rise in the future, they buy more now (demand shifts right). If they expect a recession, they may cut spending today (demand shifts left). These factors together explain why demand curves are constantly moving in real markets.
Real Example: When Tesla slashed the price of the Model 3 in 2023, demand for rival EVs from Volkswagen and Hyundai fell — their demand curves shifted left. Tesla is a close substitute, so its price cut diverted buyers away from competitors at every price point.
Exam Matters: When you explain a demand shift, always name the specific factor, state the direction of the shift, and show it on a diagram. Generic answers like "demand increased because more people wanted it" score poorly — say *why* more people wanted it.
PED measures how sensitive quantity demanded is to a price change — it is the percentage change in quantity demanded divided by the percentage change in price.
Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in the good's own price. The formula is: PED = % change in quantity demanded / % change in price. Because the demand curve slopes downward, PED is almost always negative — a price rise leads to a fall in quantity demanded.
Some examiners ignore the negative sign and work with absolute values — check your exam board's convention. What matters is the magnitude: a PED of -0.5 tells you quantity demanded is relatively unresponsive to price, while a PED of -3 tells you it is highly responsive.
Real Example: Studies of UK petrol demand consistently find a short-run PED of around -0.2. When prices spike, most drivers still need fuel to commute, so quantity demanded barely falls. This makes petrol a textbook example of price-inelastic demand.
Exam Matters: Calculation questions on PED appear frequently. Show your working clearly: state the formula, plug in the percentage changes, and interpret the result. Examiners give method marks even if the final number is wrong.
If the absolute value of PED exceeds 1, demand is elastic and a price rise cuts revenue; below 1, demand is inelastic and a price rise raises revenue.
Elastic demand (|PED| > 1) means quantity demanded is highly responsive to price. A small price rise causes a proportionally larger fall in sales. Inelastic demand (|PED| < 1) means quantity demanded is relatively unresponsive — even a big price change barely moves sales.
Most real-world goods fall somewhere between perfectly elastic and perfectly inelastic. Necessities with few substitutes (insulin, water) tend to be inelastic. Luxuries with many substitutes (a specific brand of trainers) tend to be elastic.
Real Example: Novo Nordisk can raise the price of its diabetes drug Ozempic with relatively little drop in sales because patients have few alternatives — demand is highly inelastic. In contrast, if one brand of bottled water raises its price, consumers simply switch to another brand.
Exam Matters: When interpreting PED, always state three things: the value, whether demand is elastic or inelastic, and what that means for the firm or consumer. A bare number without interpretation will not earn full marks.
Substitutes are the single biggest driver of PED — the more alternatives a consumer has, the more elastic demand becomes.
The number and closeness of substitutes is the most important determinant of PED. If many alternatives exist, consumers can easily switch when the price rises, making demand elastic. If there are few or no substitutes (insulin, petrol), consumers are trapped and demand is inelastic.
The proportion of income spent on the good also matters. A 10% rise in the price of a newspaper barely affects your budget, so demand is inelastic. A 10% rise in rent is a huge hit, so you are more likely to change behaviour — demand is more elastic.
Real Example: Philip Morris can raise cigarette prices more than most firms because nicotine addiction makes demand highly inelastic in the short run. However, over the long run, PED rises as smokers gradually quit or switch to vapes — illustrating how time increases elasticity.
Exam Matters: A common 8-mark question asks you to explain the factors that determine PED. Structure your answer around substitutes as the core driver, then layer on time, proportion of income, and habit as supporting factors. Always use a specific product example.
If demand is inelastic, raise the price to increase revenue; if demand is elastic, cut the price to increase revenue — this is the key business application of PED.
Total revenue (TR) = price x quantity. When a firm raises its price, two things happen: each unit sold earns more (pushing TR up), but fewer units are sold (pushing TR down). Which effect wins depends entirely on PED.
If demand is elastic, a price rise causes a proportionally larger fall in quantity, so total revenue falls. The smart move is to cut the price — you lose a little per unit but gain many more sales. This explains why budget airlines like Ryanair keep fares low; their customers are highly price-sensitive.
Real Example: Ryanair deliberately prices flights as low as possible because leisure travellers have elastic demand — they will switch to another airline or cancel the trip if fares rise. By cutting prices, Ryanair fills more seats and earns higher total revenue than it would at a higher fare.
Exam Matters: PED-revenue questions appear on almost every paper. Draw a quick table showing elastic vs inelastic outcomes, then apply it to the specific product in the question. Examiners reward candidates who link PED to the firm's pricing strategy.
YED measures how demand responds to a change in consumer income — the sign tells you whether the good is normal (positive) or inferior (negative).
Income elasticity of demand (YED) measures the responsiveness of demand to a change in real income. The formula is: YED = % change in quantity demanded / % change in real income. Unlike PED, the sign of YED carries crucial information — it tells you whether the good is normal or inferior.
A positive YED means the good is a normal good — demand rises when income rises. A negative YED means the good is inferior — demand falls when income rises because consumers switch to something they perceive as better.
Real Example: As UK average incomes rose through the 2010s, demand for McDonald's value-menu items stagnated while spending in mid-range restaurants grew. Value-menu items behaved as inferior goods (negative YED) — when people could afford more, they traded up.
Exam Matters: YED calculation questions test whether you can interpret the sign. State the formula, calculate the value with its sign, then classify the good as normal or inferior. A final sentence explaining what this means for the firm as incomes change earns full marks.
Luxuries have a YED greater than +1 so their demand surges as incomes rise, while necessities have a YED between 0 and +1 so demand grows slowly.
Within normal goods there is an important split. Necessities (food, basic clothing, utilities) have a YED between 0 and +1 — demand rises with income but less than proportionally. Luxuries (designer clothes, holidays abroad, fine dining) have a YED greater than +1 — demand rises more than proportionally as incomes grow.
Classifying goods this way helps you predict what happens during economic booms and recessions. In a boom, luxury firms thrive while inferior goods lose sales. In a recession, the reverse happens — budget supermarkets and own-brand products see demand rise.
Real Example: During the 2008 recession, demand for Aldi and Lidl own-brand groceries surged as household incomes fell — a classic inferior-good response. Meanwhile, premium retailer Waitrose saw sales dip, confirming that its products had a high positive YED.
Exam Matters: Context questions often describe an economic boom or recession and ask you to analyse the impact on different firms. Use YED to explain why luxury retailers suffer in recessions and why budget brands thrive. Always state the YED classification.
Firms use YED to plan product ranges and target growing markets — producing income-elastic goods is risky in recessions but highly rewarding in booms.
For businesses, YED helps with long-term planning. A firm selling luxury goods (high positive YED) should expect rapid demand growth in an expanding economy but painful drops in a recession. Diversifying into necessities (low positive YED) provides a safety net when the economy turns.
For developing countries, YED explains structural change. As national income rises, demand shifts from basic agricultural goods (low YED) towards manufactured goods and services (higher YED). Governments can use this knowledge to invest in sectors that will grow fastest as the economy develops.
Real Example: Marriott International expanded aggressively into budget hotel brands (Fairfield Inn, Moxy) alongside its luxury Ritz-Carlton line. This diversification hedges against YED risk — budget brands hold up in recessions while luxury brands capture boom-time spending.
Exam Matters: Application questions ask you to advise a firm on its product strategy using YED. Link the YED value to the economic context (boom or recession), recommend a specific action, and explain the trade-off between stability and growth potential.
XED measures how the demand for one good responds to a price change in another good — the sign tells you whether the goods are substitutes or complements.
Cross elasticity of demand (XED) measures the responsiveness of demand for Good A to a change in the price of Good B. The formula is: XED = % change in quantity demanded of A / % change in price of B. Just like YED, the sign is critical — it reveals the relationship between the two goods.
A positive XED means the goods are substitutes — when one becomes more expensive, demand for the other rises. A negative XED means the goods are complements — when one becomes more expensive, demand for the other falls because they are consumed together.
Real Example: When Sony cut the price of the PlayStation 5, demand for PS5 game titles rose sharply — a negative XED confirming they are complements. At the same time, demand for Xbox consoles dipped — a positive XED confirming PlayStation and Xbox are substitutes.
Exam Matters: Calculation questions on XED always test whether you can interpret the sign. After calculating, state whether the goods are substitutes (positive) or complements (negative), and explain what this means for the firms involved.
The closer XED is to zero, the weaker the relationship between the two goods; high positive values mean close substitutes and high negative values mean strong complements.
The magnitude of XED matters as well as the sign. A XED of +0.1 between two goods means they are weak substitutes — a price change in one barely affects demand for the other. A XED of +2.5 means they are very close substitutes — consumers switch readily between them.
Understanding the magnitude helps firms assess their competitive landscape. If your product has a high positive XED with a rival, you are in direct competition and must differentiate or compete on price. If XED is close to zero, you operate in a separate market.
Real Example: HP prices its printers cheaply but charges high prices for ink cartridges because the two are strong complements (XED is highly negative). A cheap printer locks you into buying expensive ink — a strategy only possible when XED confirms a strong complementary relationship.
Exam Matters: Higher-mark questions ask you to discuss the significance of XED for business strategy. Go beyond the sign: explain whether the relationship is strong or weak and what that means for pricing, marketing and competitive positioning.
Firms use XED to identify competitors and complementary partners, set prices strategically, and decide which markets to enter or avoid.
For pricing strategy, XED is invaluable. If your product has a high positive XED with a rival, you know that undercutting their price will attract many of their customers. If your product is a strong complement to another, you can price one cheaply to drive sales of the profitable partner (the razor-and-blades model).
For market analysis, XED helps define market boundaries. Competition regulators like the CMA use XED to determine whether two firms are in the same market — a high positive XED between their products suggests they are, which matters for merger approvals and anti-trust decisions.
Real Example: When Netflix launched in the UK, it had a high positive XED with Sky TV subscriptions. Sky responded by cutting prices and launching its own streaming service, Now TV. The high XED forced both firms into a price war that ultimately benefited consumers.
Exam Matters: Evaluate questions on XED want you to link the concept to real business or government decisions. For businesses, discuss pricing and product strategy. For governments, discuss how regulators use XED to define markets and assess competition.
Elasticities give firms the data they need to set prices, plan product ranges and forecast revenue — they turn economic theory into actionable business strategy.
PED tells a firm whether to raise or lower its price. If demand is inelastic, a price increase raises total revenue. If demand is elastic, a price cut attracts enough extra sales to more than compensate for the lower price per unit. This is why supermarkets run frequent promotions on elastic goods like branded biscuits but rarely discount inelastic staples like milk.
YED helps firms plan for the economic cycle. A luxury car manufacturer with a high positive YED should build cash reserves to survive recessions, while investing in capacity for boom periods. A firm selling inferior goods should plan for declining demand as economies grow long-term.
XED guides competitive and complementary strategy. A firm facing close substitutes must differentiate or compete on price. A firm selling complements can use loss-leader pricing on one product to drive profitable sales of the other — the classic razor-and-blades approach.
Real Example: Tesco uses Clubcard data to estimate PED for thousands of products, then prices elastic goods aggressively low to attract shoppers and inelastic goods slightly higher to protect margins. This data-driven approach to elasticity is now standard across all major UK supermarkets.
Exam Matters: Synoptic questions ask you to apply all three elasticities to a single business context. Structure your answer by covering PED (pricing), YED (product range), and XED (competitive positioning) in turn, then evaluate which is most useful for the specific scenario.
Governments use PED to design effective taxes, YED to plan public services as incomes grow, and XED to regulate competition — elasticity shapes policy.
PED and taxation: governments place indirect taxes on goods with inelastic demand (cigarettes, alcohol, petrol) because consumers cannot easily reduce consumption, so the tax raises significant revenue. Taxing elastic goods raises less revenue because consumers simply stop buying.
YED and public services: as a country's income grows, demand for healthcare and education (high YED services) rises faster than demand for basic food. Governments must plan for this structural shift by expanding service-sector capacity. In developing nations, this insight shapes long-term infrastructure investment.
XED and competition policy: regulators use XED to define relevant markets. If two products have a high positive XED, they are in the same market, so a merger between their producers may reduce competition. The CMA in the UK and the European Commission both use XED evidence in merger investigations.
Real Example: The UK government raises tobacco duty every year precisely because PED for cigarettes is around -0.4 — highly inelastic. Each price rise generates substantial tax revenue while only modestly reducing the quantity smoked, achieving both a fiscal and a public-health objective.
Exam Matters: Policy-evaluation questions ask whether a tax or subsidy will achieve its objective. Always start with PED: if demand is inelastic, the tax raises revenue but barely changes behaviour. If demand is elastic, the tax changes behaviour but raises little revenue. State this trade-off explicitly.
Traditional economics assumes consumers weigh up costs and benefits at the margin and choose the option that maximises their satisfaction.
Utility is the satisfaction a consumer gains from consuming a good — you maximise it when the last pound spent on every good gives equal marginal utility.